Electronic devices often need to generate multiple power regimes while only being powered by a single source. For example, a laptop computer may only have a single battery but may need to produce power regimes with different supply voltages for the various components on the laptop. Furthermore, regardless of the need for multiple power regimes, electronic devices often need to condition the power that is delivered to them from an external source. Returning to the example of a laptop, the laptop processor contains sensitive electronics and exhibits a widely varying power demand based on how hard the processor is working. Simply plugging in a DC version of the mains voltage source is not an option because the processor will not be shielded from dips or surges in the power supply and the power supply will likewise not be able to keep pace with the rapid transitions in the power drawn by the processor. The aforementioned requirements are addressed by power converters.
Power converters often operate with feedback loops that adjust the instantaneous performance of the power converter based on the state of the output. As a basic example, the feedback loop can detect when too much or too little power is being delivered from the supply regime to the regulated regime and accordingly decrease or increase the amount of power flowing through the power converter. In certain approaches, this feedback loop will operate in part by comparing a voltage on the output of the power converter with a reference voltage that has a known and unvarying value. The reference voltage is thereby utilized as a measuring stick to determine if the voltage of the regulated regime is remaining constant. Based on the comparison of the reference voltage and the feedback voltage, the control loop can adjust the operation of the power converter to counteract the divergence of the regulated voltage from its desired value.
A particular problem faced by power converters is referred to as an overvoltage condition. In an overvoltage condition, the voltage on the output of the converter rises outside of an acceptable degree of variation around a target voltage. For example, in a power converter designed to provide 5 volts to a regulated regime, variation of greater than 50 millivolts might be considered unacceptable. When an overvoltage condition occurs, the power converter can force itself into a state in which no power is provided from the input of the power converter to the output. However, in certain situations even this response is insufficient. Power converters often use output filters with reactive elements. These reactive elements can store power and continue to deliver that power to the regulated regime even after the power converter has been placed into a state where no additional power is being passed through the power converter. There are various approaches for detecting and responding to an overvoltage condition. Circuits directed to this problem are commonly referred to as overvoltage protection (OVP) circuits.